I want to have a go at checking and adjusting the
azimuth on my Technics RS-AZ6. Until yesterday I'd never even heard the word azimuth; so
I really am in the dark on this one and for starts I cannot even figure how to remove the
tape door.

THIS ARTICLE
explains what the azimuth adjustment is and why it is needed.

I'm afraid I
can't help with accessing the control for Your particular cassette machine, other
than to suggest that the cover door usually slides on to clips above -- but they will be
plastic and easily broken, so don't force anything!

The azimuth adjustment
is usually a small screw or allen bolt fixing one side of the rec/rep head. It will only
need a very small tweak!

I recently digitised some old tapes & realised early on that the azimuth needed
tweaking on my Yamaha deck. However out of the 2 screws for the playback head (left &
right) I had no idea from the manual which was the one for azimuth adjustment. After a
while googling I found the service manual in a downloadable .pdf - gratis.

Mine was the one on the left, yours *may* be the right, but it's worth finding out if
you don't know already - I believe the other screw is for head removal.

On some decks there is a spring pushing the head bracket up against the screw head on the
side that you adjust. Also, with door the cover off, some decks only expose the screw that
you should adjust, keeping the other side inaccessible unless you remove the whole
casing.

Remember to make sure that the screwdriver that you use is non
magnetic and has the correct tip for the screw.

When the head alignment is off, the playback is usually dull,
muffled. Pop the lid off, I don't think your model has the screw James is talking about.
IIRC, it's a recessed screw so look for a small hole near the playback head. Then you
need to figure out what screw driver type you need.

Only half joking.. they were all recorded & listened to on an Akai deck, but that
was 20 odd years ago & the sound on the Yamaha was basically muffled / lacking in top
end. The Yammie deck has a Play / Trim control which I believe offers an eq of sorts which
helped a lot, but as it was a kind of one shot deal to record them it seemed best to get
the source sounding as good as possible.

I'm never going to record tapes on it
again so messing with the azimuth for playback / archiving was a no brainer to me. The
best advice is to use your ear till it sounds the best on something like cymbals, then
you're there or thereabouts. & as Hugh said it will be just tiny tweaks either way -
if at all.

The handbook doesn't give any specific azimuth alignment details, but looking at the
mechanism exploded diapgram, the rec/rep head is fixed in place with two screws. The one
on the left is passes through a rigid collar, while the one on the right passes through a
spring -- so that's the one to tweak to tilt the head slightly one way or the other.

Quote TheBev:Oh - one last
thing, it seemed easier to judge the azimuth whilst listening in mono. I've no why this
might have been, or even if I was just kidding myself tbh but worth mentioning.

You weren't kidding yourself -- it
is the best way to do it (unless you have access to a scope or Goniometer).

The replay head has two vertical slits, one for each track of the stereo audio recorded
on the tape. If the head is tilted sideways (which is what the azimuth control adjusts),
then it will be replaying one track fractionally earlier or later than the other.

If the same material exists on both tracks, and if you mix those two tracks
together, then any time-shifting between them will result in comb filtering -- it's the
same effect as mixing the original and slightly delayed signals together that we use for
phasing, flanging, chorus etc.

However, in this case there's no modulation
going on because the time shift is fixed and static, and it won't sound hollow and phasey
because the time delay is incredibly short.

Instead, what you hear is a loss
in the extreme HF, because the first comb filter notch is just starting to impinge on the
top end of the audio bandwidth, rolling off the HF response sooner than it should.

So... the quick and dirty azimuth adjustment technique is to listen in mono and
adjust the azimuth very slightly in each direction while listening for the position that
provides the most HF (maximum brightness). When you've found that point the replay head
will be aligned to the same azimuth as the record head that made the original
recording.

Please note -- that's not necessarily the same as having a
perfectly correct (vertical) azimuth because the record head could, itself, have been
misaligned.

This is actually a significant point when adjusting cassette
machines, because the record and replay heads are usually one and the same. Consequently,
if you adjust the azimuth to optimise the replay of one cassette you are also potentially
buggering up the azimuth of anything you subsequently record!

Ideally, therefore, before making any recordings you should realign the machine's
azimuth to a known reference tape but, since they are expensive and rare, the easiest
thing to do is record your own reference tape before you start tweaking. I would suggest
recording a couple of minutes of 1kHz tone, 5kHz tone, 10kHz tone, and white noise -- in
mono on both tracks.

The white noise is the easiest thing to use for quick
resets, and the tones for precise alignment with proper test equipment. You need the 1k
and 5k tones to make sure that you don't accidently end up 360 degrees out of phase on the
10k -- which is surprisingly easy to do if you're not careful!

Of course, if
you're confident taht you'll never want to record a cassette tape ever again, then you
don't need to worry about being able to reset to the original (standard reference)
alignment.

Thanks for that Hugh - v comprehensive as always, & no
I'm confident I'll never have need to record another cassette. At least I know that I
wasn't imagining it, or worse spreading incorrect information. I've still got some more
to do myself but know that the tape is running too fast - for some reason I'm a bit *more*
apprehensive about messing with this so have been delaying.Back to the service
manual I go..

The service manual should say where the speed conetol is -- most modern cassette machines
use a servo-controlled DC motor and there will be a speed tweak somewhere -- often on or
near the motor itself.

Adjusting speed is relatively easy if you have a piano
or similar to hand and know the intended key of the music -- just adjust until sustained
notes are in tune with the piano!

In the scenario of continually matching tapes from different machines to a single playback
device, are there practical or quality advantages to be had in software correction, Rx2,
etc. (not having tried this myself)?

Quote Jeraldo:In the scenario of
continually matching tapes from different machines to a single playback device, are there
practical or quality advantages to be had in software correction, Rx2, etc. (not having
tried this myself)?

No, it
is better to align the physical heads if possible. Software correction like RX2 can
compensate for the relative delay between channels, easily, and correct the falling hf
response... But at the minor expense of increased hf noise.

In contrast,
correcting the head azimuth physically restores the hf response without increasing the
noise.

A misaligned head effectively has a wider head gap than the physical
gap and thus a poorer hf response.

Quote TheBev:I've still got some
more to do myself but know that the tape is running too fast - for some reason I'm a bit
*more* apprehensive about messing with this so have been delaying.Back to the
service manual I go..

Altering the speed is something that can be done reasonably successfully in the digital
domain if we're talking about a small difference (less than a couple of semitones). Yes,
the eq may be ever so slightly wrong and there's an extra sample rate conversion required
to do it but sample rate conversions are pretty transparent nowadays and the eq error is
going to be similar to the error due to component variations so nothing really to worry
about.

Thanks James - & Hugh again. Yeah I have altered the speed before of older tapes in
software, not because of pitch correction but because I felt the track was all the better
for a little urgency. & also if I'm honest - just because I could.

Re my apprehension of opening up the recorder, I just needed Hugh to say it was Ok.